Field of the Invention
The present invention concerns a method and apparatus for reducing the noises that occur during selective radio-frequency (RF) excitation in the acquisition of magnetic resonance (MR) data.
Description of the Prior Art
Current MR examinations are usually very loud. Depending on the type of examination and scanner, noise levels of much greater than 100 db(A) may occur, so the patient being examined has to wear hearing protection.
The main cause of the high noise level of an MR examination is the rapid switching of gradients during the examination. High noise levels occur if the timing of the pulse sequence used is very short, and high gradient moments are required. As an example in the case of slice excitation, according to the prior art the polarity of the corresponding slice selection gradient is reversed directly after a selective RF excitation so as to compensate a gradient moment that has accumulated during the RF excitation. This is also known as rephasing. In most applications, high slew rates (dG/dt) and gradient amplitudes are required for rephasing, and this results in a high noise generation.